Portugal captain Cristiano Ronaldo wore a brace on his left knee and defender Bruno Alves missed training on Friday as coach Paulo Bento prepared his injury-hit squad for their crucial World Cup clash against the U.S.

If he is unfit to face Jurgen Klinsmann's side, it would mean three of the back four who played against Germany, along with goalkeeper Rui Patricio, could miss the match.

Patricio is continuing to receive treatment for an anterior muscle problem away from the rest of the squad, while left-back Fabio Coentrao has been ruled out for the rest of the tournament with a groin injury and centre-back Pepe is suspended. Forward Hugo Almeida is also working to recover from a thigh injury away from his teammates.

Portuguese team officials dismissed reports suggesting that Ronaldo could be risking his health by playing, saying they were tired of having to deny every rumor about a player many consider to be the world's best. They noted, however, that he often plays with a brace and said he's healthy and would play against the U.S.

Teammate Helder Postiga also expressed frustration over the media circus around Ronaldo.

"I have already answered so many questions about Cristiano Ronaldo. Actually we speak about him every day. If I am sick of it, imagine how he is feeling,'' Postiga said. "If he is available enough to train with us that's probably because he is feeling well. He's been training with us all these days and as usual he always gives his best. He's just fine.''

Portugal need to beat the U.S. after their hammering by Germany in order to have a realistic chance of taking their group campaign to the last game.

Klinsmann's team, meanwhile, are in a good position after their opening 2-1 win over Ghana, sealed by a late header from substitute John Brooks, and a point could be enough for them to qualify for the round of 16 in consecutive World Cups for the first time in their history.